Update merge requests from fork project to origin project

Fix error described in https://github.com/gitlabhq/gitlabhq/issues/5185

Signed-off-by: Islam Amer <islam.amer@jollamobile.com>

Because notes scope was not limited by project in
MergeRequest#mr_and_commit_notes it causes comments from project A
appears in discussions for MR in project B.

Sort active milestones by due date (upcoming first)

Fix invalid json in API docs

Added Flowdock integration support via a service.

Make sure the flowdock-git-hook is loaded. Seems it is not autoloader, due to the gem/lib name mismatch.

Typo:Corrected the typo of sign-in in User Model

Improve 6.0-to-6.1.md update guide